Cracking promoters



United States Patent 3,287,437 CRACKING PROMOTERS Kenneth J. Frech, Kent, Ohio, assignor to The Goodyear Tire & Rubber Company, Akron, Ohio, a corporation of Ohio No Drawing. Continuation of application Ser. No. 59,205, Sept. 29, 1960. This application Apr. 19, 1965, Ser. No. 449,279

17 Claims. (Cl. 260-680) This application is a continuation of S. N. 59,205, filed September 29, 1960, and now abandoned.

This invention relates to the cracking of olefins. It also relates to a method of improving the efficiency of cracking olefins. More specifically it relates to methods of improving the efficiency of cracking of certain olefins to form specific diolefins.

It is known that certain olefins may be thermally decomposed or cracked by subjecting them to relatively high temperatures. By the terms cracking, decomposing, cracked or decomposed" as employed throughout this application and the claims appended thereto is meant that the olefin molecule splits into two or more fragments. These fragments themselves become molecules of other lower molecular weight materials. This will be explained later in greater detail. Usually the thermal decomposition or cracking of certain olefins is conducted in a closed zone or reactor at temperatures usually ranging from about 300 C. to about 1000 C. The cracking is usually done in the absence of oxygen. Olefins which crack are normally cracked while they are in a gaseous state and may be cracked either relatively pure or as mixtures with other hydrocarbons, usually in mixture with a saturated hydrocarbon, i.e. a mixed feed stream of pentene and pentane or they may be in mixture with diluents such as nitrogen, steam and the like.

Cracking of these olefins usually results in the formation of two lower molecular weight materials. The particular materials formed when these olefins are cracked depends largely upon the configuration of the olefin subjected to the cracking process. By the term configuration as used throughout this application and claims is meant the position or location of the double bonds and the position or location of the side groups, if any, of the olefin in question. To illustrate this more specifically, an olefin containing 6 carbon atoms with a side chain such as a methyl group attached to the second carbon atom of the main or straight chain portion and the double bond in the 2 position, such a material is 2-rnethyl pentene-2, when subjected to cracking, will upon decomposition produce as the predominant product the diolefin, isoprene or Z-methyl butadiene-1,3, and a lower molecular weight parafiin, methane. On the other hand, a 6 carbon olefin having a methyl group attached to the second carbon atom of the straight chain and the double bond in the 1 position, such a compound is Z-methyl pentene-l, when cracked, will produce as the predominant product two other lower molecular weight olefins, isobutylene and ethylene. These differences in product obtained upon cracking of olefins of isomeric forms of olefins are due to the fact that olefins crack at the position beta to the double bond, that is, the scission of the olefin occurs at the bond that is in a position beta to the double bond or that the split in the olefin occurs between two carbons that are second and third removed from the carbon which has the double bond attached to it. Another way of expressing this is that an olefin, if it is to crack at all, must have in its molecule a double bond which is two carbon atoms removed from another carbon to carbon bond. It is known for instance that certain olefins do not have a position beta to the double bond or they do not have a double bond which is two carbons removed from another carbon to carbon bond.

For that reason such olefins are not readily subject to cracking. Examples of these olefins which do not contain a double bond which is two carbon atoms removed from another carbon to carbon bond are ethylene, propylene, butene-Z, isobutylene, Z-methyl butene-2, and 2,3-dimethyl butene-2. Therefore, these refractory olefins are not to be included within the scope of the olefins which are to be cracked in accordance with this invention. Therefore, the configuration of the particular olefin employed in the cracking operation usually designates the main or predominant products which result from the cracking of the olefin.

Employing the most favorable conditions conducive to cracking of olefins to form lower molecular weight materials, it has been found that olefins decompose at a very low rate per pass through the cracking zone. The conditions found conducive to the cracking of olefins are the temperature, the residence time in the Zone, the ratio of the olefin to the diluent, if any, employed. It is usually the practice, to effect an increase in the overall yield of such a process, to separate the unreacted or undecomposed olefin from the products resulting from the decomposition of a portion of the olefin and return or recycle the unreacted olefin to the cracking zone. It has been found, however, regardless of how many recycles are employed the ultimate yield or the ultimate decomposition of the olefin to the desired products is not greater than about 50 mol percent of the olefin being decomposed, the remaining 50 mol percent being converted to undesirable or unwanted products as a result of side reactions caused by the high temperature, the long residence time and the recycling steps employed in the cracking process. Thereby, a fairly high percentage of the potential desired products are not obtained. Also the starting materials are wasted because they are converted to undesired products.

Therefore, this invention has as its main object a method whereby the overall yield of the desired products produced by cracking olefins may be increased. Another object is to provide a method whereby the yield per pass of desired products obtained when olefins are cracked may be increased. Another object is to increase the ultimate yield or the ultimate decomposition of olefins t0 the desired products. Still another object is to provide a method whereby the residence time of the olefins in the cracking zone may be decreased. Another object is to provide a method whereby olefins may be cracked at lower cracking temperatures. Another object is to provide a method whereby the formation of undesired products produced by side reactions during the cracking of olefins may be decreased. Another object is to provide a method whereby the size of the equipment necessary to crack a given volume of ole-fins is reduced. Another object is to reduce the amount of material required to be recycled. Still another object is to provide a method to promote the cracking of olefins to the desired products. Still other objects will appear as the description proceeds.

The objects of this invention are accomplished by subjecting olefins, which have in their molecular structure a double bond which is two carbon atoms removed from another carbon to carbon bond, to cracking conditions while said olefins are in the presence of a composition comprising bromine and at least one refractory olefin selected from the group consisting of 2,3 dimethyl butane-2; Z-methyl butene-2; isobutylene; butene-Z and propylene in which the mol ratio of bromine to refractory olefiin ranges from 10/1 to 1/25. It should be noted that ethylene, while it is a refractory olefin, is excluded from the group above, .as ethylene does not produce the desired improvement in the practice of this invention.

The bromine in the composition employed in this invention may be supplied either in gaseous form or as a liquid. In addition to bromine itself, the bromine may be supplied by means of organic or inorganic bromine-liberating compounds, i.e., a bromine precursor as it were. These bromine compounds under the conditions of the cracking operation either decompose or dissociate to produce bromine or hydrogen bromide. The reasons hydrogen bromide is mentioned, it has been found that the bro-mine, regardless of the form in which it is supplied, is in every case recovered in the eifluent stream in the form of hydrogen bromide. If an organic bromine compound is to be employed, it has been found convenient to use them by dissolving them in the olefin which is to be cracked. If inorganic bromine compounds are employed they may be dissolved in the water which is later converted into the diluent steam. These are by no means the only ways in which the bromine may be supplied to the cracking zone. Bromine either in the form of bromine or bromine compounds may also be fed to cracking zone alone or in mixture with the refractory olefins which form the other portion of the synergistic composition of this invention, or bromine or bromine compound may be supplied alone to the cracking zone where the synergistic composition may be formed in situ. Representative, but by no means all, of the bromine compounds vv hioh may be employed are ethyl bromide, 2-bromopropane, l-bromobutane, l-bromopropane, a bromotoluene, bromobenzene, l-bromo-chloromethane, 1,2-dibromoethane, hydrogen bromide, ammonium bromide and the like. Of these it is preferred to employ hydro-genbromide.

The five olefins 2,3-dimethyl butene-2; 2-methyl butene- 2; isobutylene or isobutene; butene-2 and propylene which form the other portion of the synergistic composition of this invention are refractory olefins. By the term refractory is meant that these olefins are highly resistant to decomposition by heat and are not decomposed or cracked under the conditions of the cracking process employed. For this reason they pass through the cracking process substantially unchanged in any way and hence are recoverable and reusable. The manner in which these refractory olefins .are supplied to the cracking zone has been found to be noncritical. They may be premixed with the bromine to form the synergistic composition or fed in alone to form the synergistic composition in situ, in the same manner as the bromine compound above.

While it is possible that the five refractory olefins employed as one component of the synergistic composition of this invention in situ, that is, it is possible to form them from other higher molecular weight materials which they themselves may crack under the cracking conditions of this invention to form one or more of these five refractory olefins. It is much more desirable to employ the five refractory olefins as pure hydrocarbons along with bromine to form the synergistic composition. The use of these pure refractory olefins is desirable because, if so-called precursors are employed and cracked in the process, other products are also formed which cormplicate somewhat the purification of the desired product resulting from the cracking process. Another reason why it is desirable to employ pure refractory olefins in the formation of the synergistic mixture is that the control of the amount of the refractory olefin component of the synergistic mixture is much more accurate if pure hydrocarbons are employed rather than their precursors.

Generally, the cracking of olefins in accordance with the practice of this invention may be carried out in any conventional manner usually employed in the art of cracking olefins. Generally these conditions employed may be Widely varied and are not critical. They usually depend upon the particular olefin to be cracked and the particular products which are desired. For instance, the cracking temperature may be varied widely from about 300 C. to about 1000 C. However, it is usually preferred to practice this invention at temperatures ranging between 500 and 800 C. and it is morev preferdrogen bromide.

able to employ temperatures ranging from about 625 to 725 C. The time that the olefins are in the cracking zone during the practice of this invention may range broadly from about 0.001 to about 3 seconds. However, depending upon the particular olefin cracked and the products desired, this time may vary from about 0.05 to about 1 second and it is most preferred that this time range from about 0.1 to about 0.5 second. These times are referred to usually as residence time, that is residence time within the cracking zone and are defined as the time rquired for 1 mol of incoming gas, whether it be reactant, diluent or both, to pass through the cracking zone. The cracking zone may be defined as the zone at which the temperature is elevated to the cracking temperatures as indicated above.

Generally, the olefins cracked in accordance with this invention may be in pure form or in mixture with other hydrocarbons. The olefins to be cracked may be mixed with a diluent. It is usually desirable to employ a diluent in cracking olefins in accordance with this invention. The term diluent is defined as a material which does not react or interfere with the olefin to be cracked. Likewise,

the diluent does not react with the desired products produced by thecracking at the cracking conditions employed or with composition of bromine and the refractory olefin employed as a cracking promoter. Furthermore, this diluent likewise does not crack or decompose itself at the conditions employed. Examples of diluents suitable for use in this invention are steam, carbon dioxide, hydrogen, the inert gases such as helium, neon and argon or parafiinic hydrocarbons such as methane, ethane, propane, or other hydrocarbons which themselves will not crack at the temperatures employed in the cracking conditions of this invention. The ratio of diluent to olefin to be cracked which may be employed in the practice of this invention, if any be employed, may widely vary from about 0.5/1 to about 15 or more mols of diluent permol of olefin. However, if more than about 15/ 1 ratio is employed, the improvement gained does not ofiset the cost accrued and the process could become uneconomical. Therefore, it is usually preferred to use a ratio of from about 2/1 to 4/ 1 in this invention. The diluent usually preferred in this invention is steam or water which is converted to steamat the cracking conditions. The olefins may also be cracked without diluents.

The pressure employed in the cracking zone is not critical and may vary from about 10 millimeters of mercur'y to about 500 pounds per square inch gauge. However, it is preferred to employ pressures ranging from about 1 atmosphere to about pounds per square inch gauge, with about 1 to about 2 atmospheres being most preferred, in the practice of this invention. Generally, it is preferred to employ oxygen-free conditions when practicing this invention.

As was stated above, materials which utimately yield any of the five refractory olefins may be used in mixture with the materials which yield bromine. Any brominecontaining compound may be used with a pure refractory olefin. Any of the materials which will ultimately yield one of the five olefins may be employed with pure bromine. Of the refractory materials employed to increase the efiiciency in cracking of the olefins to which this invention pertains, in accordance with this invention it is preferred to employ 2,3-dimethyl butene-2; Z-methyl butene-2; isobutylene; butene-2 and propylene in mixture with hydrogen bromide or pure bromine. It is most preferred to employ a mixture of Z-methyl butene-Z and hy- It is usually desirable to employ one of the five olefins as a pure hydrocarbon for the reason that, when precursors of these materials are employed in the cracking process of this invention there may be formed products which may cause somewhat more difiiculty in purifying the desired product. The same can be said of the bromine-containing compounds which ultimately yield bromine other than one specific brominecontaining compound, hydrogen bromide. It should be remembered that regardless of the form in which the bromine is introduced, in the practice of this invention it is always found in the efiiuent from the cracking zone in the form of hydrogen bromide. Therefore, it is usually desirable to employ hydrogen bromide as a starting material to supply the bromine. The difficulty in purification can be illustrated, for instance, if the precursor Z-methyl pentene-l is employed to produce the refractory olefin isobutylene. This precursor forms not only isobutylene which, when combined with the bromine, aids in the cracking of the olefins of this invention; but, in addition, this 2-methyl pentene-l also forms ethylene which must be separated from the desired product causing additional difiiculty in the purification step. Some of these olefin precursors, of course, may be desirable to employ in conjunction wtih bromine in that they produce, when cracked, two of the desired refractory olefins. For instance, Z-methyl hexene-l, when subjected to the cracking conditions employed, produces one mol each of isobutylene and propylene. Also certain other materials such as hexene-l, when cracked, produces 2 mols of propylene. Also materials such as heptene-l can crack to propylene and butene-l and then on a second pass through a cracking zone, or maybe even in the first pass, the butene-l will then crack to produce a mol of propylene. Thus, it can be seen that it may well be desirable, rather than detrimental, to employ certain selected precursors of these refractory olefins along with bromine in the practice of this invention. However, even in view of this advantage, it still may be desirable to employ the olefins as pure olefins because the amounts may be controlled wtih a greater degree of accuracy. The amount of synergistic material employed in the practice of this invention may become a factor in the economy of such a process.

The amount of synergistic composition comprising bromine and at least one olefin selected from the group consisting of 2,3-dimethyl butene-Z; 2-methyl butene-2; isobutylene; butene-Z and propylene which is employed in the practice of this invention has not been found to be critical. The mol percent employed, based on the amount of olefin to be cracked, may vary from a low of about 0.4 to about 50 mol percent bromine and from a low of about 0.1 to a high of about 50 mol percent of the refractory olefin. It has been found, however, that the most preferred ranges are from about 2 to mol percent of bromine and from about 2 to 10 mol percent refractory olefin. Thus, the combined components range from 4 to 20 mol percent. As was stated previously, the mol ratio of bromine to olefin may vary broadly from about 10/1 to about l/25. It has been found preferred to employ the mol ratios of bromine to refractory olefin ranging from about 2/1 to about l/2.

While it is possible to promote the cracking of all olefins regardless of their configuration, so long as they have in their structure a double bond which is two carbon atoms removed from another carbon to carbon bond, by the practice of this invention, it is most desirable to employ the process of this invention with olefins which have the proper configuration so that they will crack to form predominantly a diolefin.

Representative among the olefins which will decompose to form predominantly butadiene-1,3 when cracked in accordance with the practice of this invention are pentene- 2; hexene-Z; 3-methyl pentene-l; cyclohexene; 3-methyl butene-l; Z-heptene; 3-methyl hexene-l; S-methyl hexene- 2; 2-octene; S-methyl heptene-Z; 3,5-dimethyl hexene-l; 3,4,4-trimet-hyl pentene-l; 6-methyl heptene-2; nonene-2; and 3-methyl octane-1.

Representative among the olefins which will decompose to form predominantly 2-methyl butadiene-1,3, or isoprene when cracked in accordance with the practice of this invention are Z-methyl pentene-Z; 3-methyl pentene-Z; 2-ethyl butene-l;

3 ,3 -dimethylbutene-1 2,3-dimethyl butene-l; 2-methyl hexene-2; 3-methyl hexene-Z; 2-ethyl pentene-l; 2,3-dimethyl pentene- 1 3,3-dimethyl pentene-l; Z-methyl heptene-Z; 3-methy1 heptene-Z; 2-ethyl hexene-l; 3,3-dimethyl hexene-l; 2,5-dimethyl hexene-Z; 3,5-dimethyl hexene-2; 4-methyl-2-ethyl pentenel; 2,3,4-trimethyl pentene-l; 3,3,4-trimethyl pentene-Z; Z-methyl octene-2; 3-methyl octene-2; 3,3-dimethyl heptene-l; 2,5-dimethyl heptene-2; 2,6-dimethyl heptene-Z; S-methyI-Z-ethyl hexene-l; 3,3,5-trimethyl hexene-l; and 2,5,5-trimethyl bexene-Z.

Representative among the olefins which will decompose to form predominantly 2-ethyl butadiene-1,3 when cracked in accordance with the practice of this invention are 3-ethyl pentene-Z; 2-ethyl pentene-2; 3-ethyl hexene- 2; 3-methyl-2-ethyl pentene- 1 Representative among the olefins which will decompose to form predominantly 2,3-dimethyl butadiene-1,3 when cracked in accordance with the practice of this invention are 2,3-dimethyl pentene-Z; 3-methyl-2-ethyl butene-l; 2,3,3-trimethy1 butene-l; 2-isopropyl pentene-l; 2,3,3-trimethyl pentene-l; and 2,3-dimethyl heptene-2.

Representative among the olefins which will decompose to form predominantly 3-methyl pentadiene-l,3 when cracked in accordance with the practice of this invention are 3-methyl hexene-3; 3-methyl heptene-3; 3,4-dimethyl hexene-Z; 3,6-dimethyl heptene-3.

Representative among the olefins which will decompose to form a predominantly Z-methyl pentadiene-1,3 and 4-methyl pentadiene-1,3 when cracked according to the practice of this invention are 2,4-dimethyl pentene-2; Z-methyl heptene-3; 4,4-dimethyl hexene-Z; 2-propyl pentene-2; Z-methyl-S-ethyl pentene-l; 2,6-dirnethyl heptene- 3 and 2-propyl hexene-l.

Representative among the olefins which will decompose to form predominantly piperylenes when cracked in accordance with the practice of this invention are hexene-3; 4-methyl pentene-2; heptene-3; 4-methyl hex ene-2; octene-3; 4-methyl heptene-2; 6-methyl heptene-3; 3-ethyl hexene-l; 4-methyl-3-ethy1 pentene-Z; 4,5-dirnethyl heptene-2; and 4,5,5-trimethyl hexene-2.

The specific examples of olefins listed above are intended to be representative only and by no means limiting of the olefins which may be employed in the practice of this invention. They are intended only to il1us trate that certain olefins may be cracked in the presence of a synergistic composition comprising bromine and/0r bromine containing compounds in admixture with at least one olefin selected from the group consisting of 2,3- dimethyl butene-2; 2-methyl butene-2; isobutylene; butene- 2 and propylene and/or precursors thereof to form diolefins, Other olefins which produce two olefins upon cracking may also be promoted in a cracking process by the use of the synergistic composition of this invention.

The practice of this invention is illustrated by the following examples which are intended to be representative rather than restrictive of the scope of this invention.

All of the experiments were performed in a cracking assembly consisting of a hairpin coil prepared from inch OD. 316 stainless steel tubing. This cracking coil was immersed in a bed of fluidized heat transfer powder. This heat transfer powder was a microspheroidal aluminasilica material normally employed as a cracking catalyst. This heat transfer powder was heated both by an electrical resistance heater and by combusting a natural gas flame directly in the fluidized powder bed. The temperature gradient from the top to the bottom of the bed was never more than about to 6 C. and the gradient from the fluidized bed to the cracking zone was never more than about 5 to 6 C. The temperatures were measured within the fluidized bed by means of conventional thermocouple techniques. The cracking coil had conventional thermocouple wells and the temperature within the cracking zone was also measured by conventional thermocouple techniques. The procedure employed was to bring the heat transfer powder up to about 500 C. by employing the electrical resistance heaters, at the same time fluidizing the bed by means of air. Then a direct natural gas/air flame was employed to bring the heat transfer bed up to the desired cracking or operating temthe residence time reported in seconds, column 5the temperature reported in degrees centigrade at which the cracking took place, column 6the yield reported in percent and represents the total feed stock decomposed to the desired product per pass, column 7 cracking efliciency reported in percent and represents the total olefin feed stock decomposed to the desired product employing recycle techniques for the olefin feed stock unreacted during each pass.

Example I In Example I, Run No. 1 illustrates the effect of 2- methyl butene-Z alone upon the cracking of Z-methyl pentene-Z to isoprene. Run No. 2 of this example illustrates the efiect of hydrogen bromide alone on the oracking of 2-methyl pentene-Z to isoprene. Run No. 3 of this example, which combines 2-methyl butene-Z with hydrogen bromide to form a synergistic composition, illustrates the practice of this invention in the cracking of Z-methyl pentene-Z to form isoprene. Run No. 3 shows the advantage obtained by this synergistic composition over the use of either component alone, as in Runs 1 and 2.

FEED STO CK-iZ-METHYL PENTENE-Z PRODUCT-ISOPRENE Residence Temper- Run Promoter Used Amount, Time, ature, Yield, Efiieieney No. Moi Percent Seconds C.

1 2-methyl butene 2 6 0.101 652.0 10.9 54.3 g gydiggelnbbiomige 5 0.0898 646.9 23.7 59.7

me y 11 ene- 6 Hydrogen 5 0. 098 650 28.2 65.8

perature. The natural gas flame and products of the Example 11 combustion and additional air were used to fluidize the powdered bed. The promoter that was a refractory olefin was mixed with the olefin which was to be cracked, in the desired mol percentage prior to the olefin being passed through the cracking zone. Water was passed to a pre heater and converted to steam. The olefin containing the promoter was pumped at the proper rates necessary to produce the desired steam to hydrocarbon ratios and at an overall rate to give the desired residence time of the materials in the cracking zone. To the steam was added the hydrogen bromide in the form of anhydrous gas in the proper mol ratio. The steam to hydrocarbon ratio employed was 3/ 1. When all variables had been adjusted to give the desired operating conditions, the

In Example II, Run No. 1 illustrates the effect of hydrogen bromide alone upon the cracking of a mixture of 51% 3-methyl pentene-2 and 49% Z-methyl pentene-2 to isoprene; Run No. 2 represents the efiect of 2.,3-dimethyl butene-2 alone upon the cracking of a mixture of 53% 3-methyl pentene-Z and 47% Z-methyl pentene-2 to isoprene. Run No. 3 illustrates the same as Run No. 2 at slightly different reaction conditions. Run No. 4 and Run No. 5 represent the practice of this invention in that here 2,3-dimethyl butene-2 and hydrogen bromide are employed to form a synergistic composition in the cracking of a mixture of 53% 3-methyl-pentene-2 and 47% Z-methyl pentene-Z to isoprene.

FEED STOCK-MIXTURES OF 2-METHYL PENTENE-2 AND 3-METHYL PE NTE NE-2 PRODUOT-ISOPRENE products of the cracking were collected; if liquid, by means of cooled receivers, and if gas, they were metered at atmospheric pressure and room temperature conditions. The products collected were analyzed for content and yields by conventional analytical methods. Conventional recycle techniques were employed to obtain the ultimate yields and are reported as ultimate reaction efficiencies. The per pass yields are reported as the yield per pass.

The results of each of the runs in each example, as well as the operating conditions, the promoter employed and the amounts of promoter employed are listed in table form. Column 1 designates the run number, column 2the promoter employed, column 3the amounts of promoter employed, reported in mol percent based on the total olefin feed stock to be cracked, column 4-- The examples above illustrate the synergistic effect obtained by the practice of this invention. In Example 1 it may be observed that, employing the synergistic composition Z-methyl butene-Z and hydrogen bromide in a feed stock of 2-methyl pentene-Z (Run No. 3), more than increase in the yield of isoprene per pass is obtained over the Z-methyl butene-Z alone (Run No. l) and more than 19% increase in the yield of isoprene per pass is obtained over hydrogen bromide alone (Run No. 2). Also, a most startling effect illustrated by the use of the synergistic compositions of this invention is evidenced by a comparison of the efliciences obtained in the production of i-soprene from a feed stock of Z-methyl pentene-2 wherein the use of Z-methyl butene-Z and bydrogen bromide as a synergistic promoter is employed. This shows a 21% increase over one-component promoter alone, such as 2-rnethyl butene-Z (Run No. 1) and a increase over the other one-component promoter alone such as hydrogen bromide (Run No. 2). Thus,

it can be seen from these results that the use of the synergistic compositions of this invention are preferred over either of the other two components when employed separately. Similar results are obtained in mixed feed stocks as shown in Example 2. Similar results may be obtained employing other synergistic compositions as defined in this application with other olefins previously described while employing various other cracking conditions.

While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

What is claimed is:

1. A process to produce isoprene which comprises mixing (1) at least one olefin selected from the group consisting of Z-methyl pentene-Z; S-methyl pentene-Z; Z-ethyl butene-l; 3,3-dimethyl butene-l; 2,3-dimethyl butene-l; 2-methyl hexene-2; 3-methyl hexene-Z; and 3,3-dirnethyl pentene-l, and (2) about 4 to about mol percent, calculated on the total mols of olefins, of a promoter comprising a. mixture of bromine and at least one refractory olefin selected from the group consisting of 2,3-dimethyl butene-2; 2-rnethyl butene-2 and isobutylene in which the mol ratio of bromine to said refractory olefin ranges from about 10/1 to about 1/25, subjecting the resulting mixture to temperatures ranging between 500 C. and 800 C. for times ranging from about 0.05 to about 1 second and at pressures not exceeding about 100 pounds per square inch, to cleave the carbon-to-carbon single bond which is in the position beta to the double bond of said olefin in (1) above, to form isoprene and recovering said isoprene.

2. The method according to claim 1 in which, in the composition, the bromine is supplied by means of hydrogen bromide and in which the refractory olefin is Z-methyl butene-Z.

3. The method according to claim 1 in which, in the composition, the bromine is supplied by means of hydrogen bromide and the refractory olefin is 2,3-dimethyl butene-Z.

4. The method according to claim 1 in which the olefin to be cracked is 3-methyl pentene-Z.

5. The method according to claim 1 in which the olefin to be cracked is 2-methyl pentene-2.

6. The method of preparing isoprene which comprises demethanating Z-methyl pentene-2 While in the presence of a mixture comprising hydrogen bromide and 2-methyl butene-Z, wherein the mol ratio of hydrogen bromide to Z-methyl butene-2 is about 2/1 to about l/2 and the amount of each of hydrogen bromide and 2-methyl butene-2 ranges from about 2 to 10 mol percent calculated on the mols of Z-methyl pentene-2, said demethanation process being conducted at temperatures ranging between 500 C. and 800 C. and for times ranging from about 0.05 to about 1 second and at pressures not exceeding about 100 pounds per square inch gauge, to cleave the carbon-to-carbon single bond which is in the position beta to the double bond of said Z-methyl pentene-Z to form isoprene and recovering said isoprene.

7. A process to produce 2-ethyl butadiene-1,3 which comprises mixing 1) at least one olefin selected from the group consisting of 3-ethy1 pentene-Z; 2-ethyl pentene-2; and 3-ethy1 hexene-2; and (2) about 4 to about 20 mol percent, calculated on the total mols of olefins, of a promoter comprising a mixture of bromine and at least one refractory olefin selected from the group consisting of 2,3-dimethyl butene-2; 2-methyl butene-2 and isobutylene in which the mol ratio of bromine to said refracto-carbon single bond which is in the position beta to the double bond of said olefin in (1) above, to form Z-ethyl butadiene-l,3 and recovering said 2-ethyl butadiene-1,3.

8. The method according to claim 7 in which, in the composition, the bromine is supplied by means of hydrogen bromide and in which the refractory olefin is 2-methyl butene-Z.

9. The method according to claim 7 in which, in the composition, the bromine is supplied by means of hydrogen bromide and the refractory olefin is 2,3-dimethy1 butene-Z.

10. The method according to claim 7 in which the olefin to be cracked is Z-ethyl pentene-2.

11. The method according to claim 7 in which the olefin to be cracked is 3-ethyl pentene-Z.

12. A process to produce piperylene which comprises mixing (1) at least one olefin selected from the group consisting of hexene-3; 4-methyl pentene-Z; heptene-3; and 4-methyl hexene-2, and (2) about 4 to about 20 mol percent, calculated on the total mols of olefins, of a promoter comprising a mixture of bromine and at least one refractory olefin selected from the group consisting of 2,3-dimethyl butene-Z; Z-methyl butene-Z and isobutylene in which the mol ratio of bromine to said refractory olefin ranges from about 10/1 to about 1/25, subjecting the resulting mixture to temperatures ranging between 500 C. and 800 C. for times ranging from about 0.05 to about 1 second and at pressures not exceeding about pounds per square inch, to cleave the carbonto-carbon single bond which is in the position beta to the double bond of said olefin in (1) above, to form piperylene and recovering said piperylene.

13. The method according to claim 12 in which, in the composition, the bromine is supplied by means of hydrogen bromide and the refractory olefin is Z-methyl butene-2.

14. A process to produce 2,3-dimethyl butadiene-1,3 which comprises mixing (1) at least one olefin selected from the group consisting of 2,3-dimethyl pentene-Z; 3- rnethyl-Z-ethyl butene-l; 2,3,3-trimethyl butene-l and 2,3,3-trimethyl pentene-l; and (2) about 4 to about 20 mol percent, calculated on the total mols of olefins, of a promoter comprising a mixture of bromine and at least one refractory olefin selected from the group consisting of 2,3-dimethyl butene-Z; 2-methyl butene-Z and isobutylene in which the mol ratio of bromine to said refractory olefin ranges from about 10/1 to about 1/25, subjecting the resulting mixture to temperatures ranging between 500 C. and 800 C. for times ranging from about 0.05 to about 1 second and at pressures not exceeding about 100 pounds per square inch, to cleave the carbonto-carbon single bond which is in the position beta to the double bond of said olefin in 1) above, to form 2,3-dimethyl butadiene-l,3 and recovering said 2,3-dimethyl butadiene-1,3.

15. The method according to claim 14 in which, in the composition, the bromine is supplied by means of hydrogen bromide and the refractory olefin is 2-methyl butene-Z.

16. A process to produce 3-methyl pentadiene-l,3 which comprises mixing (1) at least one olefin selected from the group consisting of 3-methyl hexene-3; 3-methyl heptene-3; and 3,4-dimethyl hexene-2, and (2) about 4 to about 20 mol percent, calculated on the total mols of olefins, of a promoter comprising a mixture of bromine and at least one refractory olefin selected from the group consisting of 2,3-dimethyl butene-Z; Z-methyl butene-Z and isobutylene in which the rnol ratio of bromine to said refractory olefin ranges from about 10/1 to about 1/25, subjecting the resulting mixture to temperatures ranging between 500 C. and 800 C. for times ranging from about 0.05 to about 1 second and at pressures not exceeding about 100 pounds per square inch, to cleave the carbon-to-carbon single bond which is in the position beta to the double 'bond of said olefin in 1) above, to form 3-metl1yl pentadiene-1,3 and recovering said 3-methyl pentadiene-1,3.

17. A process to produce Z-methyl pentadiene-L?! and 4-methy1 pentadiene-L3 which comprises mixing (1) at least one olefin selected from the group consisting of 2,4- dimethyl pentene-Z; Z-methyl heptene-S and 4,4-dimethyl hexene-Z and (2) about 4 to about 20 mol percent, calculated on the total :mols of olefins, of a promoter comprising a mixture of bromine and one refractory olefin selected from the group consisting of 2,3-dimethyl butene- 2; Z-methyl butane-2 and isobutylene in which the mol ratio of bromine to said refractory olefin ranges from about 10/1 to about l/25, subjecting the resulting mixture to temperatures ranging between 500 C. and 800 C. for times ranging from about 0.05 to about 1 Second 12 and at pressures not exceeding about 100 pounds per square inch, to cleave the tcarbon-to-carbon single bond which is in the position beta to the doubel bond of said olefin in (1) above, to form Z-methyl pentadiene-1,3 and 4-methyl pentadiene-L3 and recovering said Z-methyl pentadiene-1,3 and 4-methyl pentadiene-1,3.

References Cited by the Examiner UNITED STATES PATENTS 2,370,513 2/1945 Amos et al. 260680 2,391,158 12/1945 Hepp 260 6s0 2,397,638 4/1946 Bell et al. 260-683 X 3,104,269 9/1963 Schaffel 260-680 FOREIGN PATENTS 588,870 7/1960 Belgium.

807,149 1/1959 Great Britain.

868,566 5/1961 Great Britain.

PAUL M. COUGHLAN, ]R., Primary Examiner. 

1. A PROCESS TO PRODUCE ISOPRENE WHICH COMPRISES MIXING (1) A LEAST ON OLEFIN SELECTED FROM THE GROUP CONSISTING OF 2-METHYL PENTENE-2;3-METHYL PENTENE-2;2ETHYL BUTENE-1;3,3-DIMETHYL BUTENE-1; 2,3-DIMETHYL BUTENE-1; 2-METHYL HEXENE-2; 3-METHYL HEXENE-2; AND 3,3-DIMETHYL PENTENE-1, AND (2) ABOUT 4 TO ABOUT 20 MOL PERCENT, CALCULATED ON THE TOTAL MOLS OF OLEFINS, OF A PROMOTER COMPRISING A MIXTURE OF BROMINE AND AT LEAST ONE REFRACTORY OLEFIN SELECTED FROM THE GROUP CONSISTING OF 2,3-DI METHYL BUTENE-2; 2-METHYL BUTENE-2 AND ISOBUTYLENE IN WHICH THE MOL RATIO OF BROMINE TO SAID REFRACTORY OLEFIN RANGES FROM ABOUT 10/1 TO ABOUT 1.25 SUBJECTING THE RESULTING MIXTURE TO TEMPERATURE RANGING BETWEEN 500* C. AND 800*C. FOR TIMES RANGING FROM ABOUT 0.05 TO ABOUT 1 SECOND AND AT PRESSRES NOT EXCEEDING ABOUT 100 POUNDS PER SQUARE INCH, TO CLEAVE THE CARBON-TO CARBON SINGLE BOND WHICH IS IN THE POSITION BETA TO THE DOUBLE BOND OF SAID OLEFIN IN (1) ABOVE, TO FORM ISOPERENE AND RECOVERING SAID ISOPERENE. 